This invention relates to a pliers adapted to have firm gripping engagement with a range of different size nuts and bolts.
A conventional pliers includes two pivotably connected handle members having opposed facing jaws adapted to grip a nut or bolt therebetween. The jaw surfaces enjoy firm gripping contact with the nut or bolt only when the jaw surfaces are parallel. For a given pivotal connection of the two handle members the desired parallelism is only possible for one particular size nut or bolt; for other nut or bolt sizes the jaw surfaces are acutely angled to one another so that they do not have firm flatwise contact with the flats on the nut or bolt. As a result, the pliers tend to slip on the nut or bolt when a turning torque is applied to the handle portions of the pliers.
U.S. Pat. No. 1,561,833 to A. Cruickshank shows a pliers having one of its jaws constructed as an adjustable jaw element pivotably attached to one of the pliers handle members. The pivotal nature of the jaw element enables the work-engagement surface of the jaw element to be parallel with the opposed work-engagement surface of the other jaw element when the jaw elements have various different spacings. The pliers can therefore maintain a firm flatwise gripping engagement with a range of different sized nuts or bolts.
The pivotal jaw element in U.S. Pat. No. 1,561,833 is disclosed as having a loose pivotable fit in the associated handle member in order that stresses associated with the gripment process will be transmitted onto an enlarged bearing surface concentric with the pivot pin. In service, the pivotable jaw would tend to swing or flip-flop in a relatively uncontrolled manner while the pliers was being removed from one set of flats on the work and transferred to another set of flats. It is believed that this would be disconcerting to the user. Also, it might make it somewhat more difficult to place the pivotal jaw against the flat on the work.
The present invention contemplates a pliers somewhat similar to the pliers shown in U.S. Pat. No. 1,561,833, but without the loose pivotal swinging motion associated with the patented arrangement. In the proposed pliers the pivotal jaw has a relatively large diameter semi-circular bearing surface engaged with a mating concave bearing surface on the pliers arm structure. A small diameter circular pin extends through a slot in the pivotal jaw to swingably retain the jaw on the arm structure. The pin has a close sliding fit on the slot walls, such that the bearing surfaces are frictionally maintained in any given position in the absence of an applied force. The jaw can pivot, but without the uncontrolled flip-flop action that is apparently produced with the earlier patented arrangement.